Tomato bacterial canker, caused by Gram-positive bacterium Clavibacter michiganensis subsp. michiganensis (Cmm), is one of the most important diseases of tomato in temperate zones and greenhouses worldwide (Gleason M L, et al., Recent progress in understanding and controlling bacterial canker of tomato in Eastern North America. Plant Dis. 1993, 77:1069-1076). Cmm infects the plant through wounds and via natural openings, such as stomata and hydathodes, after which it moves into xylem (Carlton W M, et al., Ingress of Clavibacter michiganensis subsp. michiganensis into tomato leaves through hydathodes. Phytopathology 1998, 88:525-529; Gartemann K H, et al., Clavibacter michiganensis subsp. michiganensis: first steps in the understanding of virulence of a Gram-positive phytopathogenic bacterium. J. Biotechnol. 2003, 106:179-191). Bacterial canker causes plant wilting and death, “bird's eye” lesions on the fruit (field) or netting (greenhouse), and reduced fruit set and size, which leads to severe yield loss, which can be as high as 84% in commercial fields and 93% in controlled studies. In the U.S., the economic loss due to bacterial canker reaches 25-30% in greenhouse tomato production.
The pathogen Cmm is seed-transmitted and infested seed and seedlings are considered the primary source of inoculum. It is known that Cmm is a strong endophyte and is easily disseminated directly into vascular tissue during transplanting, pruning, and harvesting under current tomato production systems (Chang R J, et al., Dissemination of Clavibacter michiganensis subsp. michiganensis by practices used to produce tomato transplants. Phytopathology. 1991, 81:1276-1281).
At present, control of tomato bacterial canker mainly relies on use of clean seed, healthy transplants and crop rotation. Once the disease is established in a field or greenhouse, however, chemical treatment such as copper-based bactericides or antibiotics has limited effect in reducing the disease (Hausbeck M J, et al., Effect of bactericides on population sizes and spread of Clavibacter michiganensis subsp. michiganensis on tomatoes in the greenhouse and on disease development and crop yield in the field. Phytopathology. 2000, 90:39-44; Miller, S. A., et al., Hot water and chlorine treatment of vegetable seeds to eradicate bacterial plant pathogens. The Ohio State University Extension. HYG-3085-05, 2005). Meanwhile, the development of bactericide resistance in plant pathogenic bacteria is increasing (Cooskey D A, Genetic of bactericide resistance in plant pathogenic bacteria. Annu. Rev. Phytopathology. 1990, 28:201-219).
Other subspecies of Clavibacter michiganensis are problematic for a variety of other economically important plants. For example, Clavibacter michiganensis subsp. nebraskensis, which affects maize, Clavibacter michiganensis subsp. phaseoli subsp. nov., which affects beans, Clavibacter michiganensis subsp. sepedonicus, which affects potatoes, Clavibacter michiganensis subsp. tesselarius, which affects wheat, and Clavibacter michiganensis subsp. insidiosus, which affects alfalfa, all present challenges that need addressing.
Therefore, new chemicals with unique targets or target pathways are urgently required for management of Clavibacter michiganensis infections. The compositions and methods disclosed herein address these and other needs.